Gas turbine engines of all types experiences changes in power levels. Normally, these changes in power level involve acceleration, or deceleration, of each turbine and associated compressor. These changes in power level take a finite amount of time. The time is determined by the inertia of each turbine and associated compressor and by limitations on the change in fuel flow rate allowed to avoid compressor surge, over temperature or extinction of combustion in the combustor.
In industrial gas turbine engines very fast reductions in power level are required if there is a loss of load, an emergency shut down or a shaft breakage. If the gas turbine engine includes a heat exchanger to transfer heat from the exhaust gases to the air entering the combustor, the heat transferred by the heat exchanger to the air entering the combustor cannot be turned off easily.
Recuperated gas turbine engines use heat exchangers to return heat from the final turbine exhaust to pre-heat compressed air entering the combustor. This helps to conserve fuel by raising the combustor air temperature and therefore limiting the amount of fuel needed to achieve the turbine inlet temperature.